A novel sensing strategy for the detection of Staphylococcus aureus DNA by using a graphene oxide-based fluorescent...

A novel sensing strategy for sequence-specific recognition of Staphylococcus aureus (S. aureus) DNA was designed based on the DNA hybridization between dye-labeled single-stranded DNA (ssDNA) and the complementary target DNA. Graphene oxide (GO) can adsorb FITC-labeled probes and quench the fluorescence efficiently via Förster resonance energy transfer (FRET). However, the formation of double-stranded DNA (dsDNA) will alter the conformation of ssDNA and disturb the interaction between GO and ssDNA. Thus the dsDNA-GO mixture exhibits a stronger fluorescence emission than that of the ssDNA-GO mixture, and the relative fluorescence intensity ΔI/I0 (ΔI = I(a) - I(q)) is related to the concentration of ssDNA (S. aureus DNA). Here we illustrate a "post-mixing" strategy in which the fluorescent dye-labeled DNA was allowed to hybridize with S. aureus DNA prior to the addition of GO. In this experiment, the competition between ssDNA-GO adsorption and the dsDNA formation was avoided and the incubation time was shortened to 20 min. Under the optimum conditions, the relative fluorescence intensity ΔI/I0 was proportional to the concentration of S. aureus DNA in the range 0.0125-3.125 nmol L(-1), with a detection limit of 0.00625 nmol L(-1) and good sequence selectivity.